CN105134618B - A kind of centrifugal pump control method based on the analysis of pressure fluctuation time-frequency characteristic - Google Patents

Abstract

The invention relates to the field of centrifugal pump operation monitoring, and relates to a centrifugal pump adjustment method based on the time-frequency characteristic analysis of pressure pulsation. The method includes the following steps: (a) collecting the pressure pulsation of the pump cavity, and obtaining the time domain of the pressure pulsation; (b) analyzing the frequency spectrum of the pressure pulsation; (c) analyzing the broadband frequency characteristic of the pressure pulsation; (d) analyzing the characteristic of the broadband frequency component changing with time ; (e) Analysis of the vortex in the cavity of the centrifugal pump; (f) Adjustment of the running state of the centrifugal pump. By analyzing the time-frequency characteristics of the pressure pulsation, the present invention can judge whether there is a flow phenomenon such as vortex or vortex belt inside the centrifugal pump, can judge whether the vortex moves, and can regularly and quantitatively reflect the change of the vortex shape in the pump chamber, which can ensure the centrifugal pump The vortex flow at the pump inlet is in a relatively ideal state, thereby prolonging the service life of the centrifugal pump, ensuring the high efficiency of the centrifugal pump and saving energy consumption.

Description

A Centrifugal Pump Regulation Method Based on Time-Frequency Analysis of Pressure Fluctuation

technical field

The invention relates to the field of centrifugal pump operation monitoring, and relates to a centrifugal pump adjustment method based on the time-frequency characteristic analysis of pressure pulsation.

Background technique

The number and installed power of water pumps in my country rank first in the world. According to statistics, the total installed power of pumps exceeds 950 million kW, and the annual power consumption tends to be nearly 530 billion kW·h, accounting for about 16% of the country's total power generation. Among all kinds of pump types, the number of centrifugal pumps accounts for more than 85%, which are widely used in water conservancy, aerospace, electric power, petrochemical and other fields, and play a vital role in the national economy.

Generally speaking, once a centrifugal pump is in operation, it will inevitably produce pressure pulsations that vary with time. Pressure pulsation is one of the important reasons that lead to accelerated wear of pump blades, increased vibration, increased noise, reduced water supply capacity, and reduced operating efficiency. development bottleneck. At present, the evaluation of pump pressure pulsation is mainly carried out from two perspectives of time domain statistics and frequency domain analysis. -1997), the corresponding Chinese standard is "Hydraulic Machinery Vibration and Pulsation Field Test Regulations" (GB 17189-1997). For the pressure pulsation frequency domain analysis method, it is limited to fast Fourier transform (FFT) analysis method, mainly focusing on the evaluation of single frequency components such as main frequency and sub-dominant frequency, such as leaf frequency, shaft frequency and cavitation low frequency.

However, the pressure pulsation of the centrifugal pump may also have a continuous frequency band with high pressure amplitude, which appears as a "hill" in the frequency domain diagram. So far, no scholars have conducted in-depth research on this frequency component with broadband characteristics, and the existing pressure pulsation system cannot evaluate this frequency component. In addition, the use of the FFT transformation method is based on the assumption that the collected pressure pulsation data is a stationary signal, which is a global transformation, and the frequency domain results obtained by this method do not include time information. Therefore, it is generally considered that the frequency components in the frequency domain diagram do not change with time. With the in-depth understanding of the internal flow field of the centrifugal pump, many studies have found that even at the design point, there will still be a vortex that changes with time and space in the semi-spiral suction chamber or the spiral pressure water chamber of the double-suction centrifugal pump. The shape of these vortices changes with time, and even wanders. When the centrifugal pump deviates from the rated operating conditions, the vortex flow state in the suction chamber or inlet pipe will be more prominent. How to quantitatively analyze and monitor these phenomena has become an urgent problem to be solved.

Therefore, in order to reveal the complex frequency components in the centrifugal pump cavity and the phenomenon that the vortex shape changes with time, it is very necessary to introduce a new method with broadband frequency quantitative analysis and frequency component analysis with time.

Contents of the invention

The purpose of the present invention is to provide a centrifugal pump adjustment method based on the time-frequency characteristic analysis of pressure pulsation with quantitative analysis of broadband frequency and analysis of its frequency components changing with time, that is, to quantitatively extract the characteristic frequency of pressure pulsation of the vortex in the centrifugal pump cavity, and then By analyzing the frequency characteristic components and their changing characteristics with time, using this method can ensure that the vortex flow at the inlet of the centrifugal pump is in an ideal state, thereby prolonging the service life of the centrifugal pump, ensuring that the centrifugal pump has high efficiency and saving energy consumption.

In order to achieve the above object, the present invention provides the following technical solutions:

The invention provides a centrifugal pump adjustment method based on the time-frequency characteristic analysis of pressure pulsation, the method includes the following steps:

(a) Acquisition of pressure pulsation in the pump chamber to obtain the time domain of pressure pulsation:

A pressure pulsation sensor is installed at the detection position of the centrifugal pump. The pressure pulsation sensor outputs the water pressure pulsation signal to the acquisition card and converts it into a digital signal through a processor connected to the acquisition card. The digital signal is the pressure pulsation time domain of the detection position of the centrifugal pump. ;

(b) Spectrum analysis of pressure pulsation:

Perform FFT transformation on the pressure pulsation time domain of the detection position of the centrifugal pump obtained in step (a), to obtain the pressure pulsation frequency domain;

(c) Analysis of pressure pulsation broadband frequency characteristics:

Carrying out Gaussian distribution envelopment to the continuous low-frequency broadband components with high pressure amplitude in the pressure pulsation frequency domain obtained in step (b), and fitting to obtain the center frequency and broadband frequency;

(d) Analysis of the characteristics of broadband frequency components changing with time:

Carry out adaptive optimization and time-frequency distribution on the broadband frequency obtained in step (c), obtain the change of frequency and its amplitude in time, and extract the frequency components whose amplitude is greater than 50% to 70% of the highest intensity level as ridge information , to get the variation relationship of its frequency components with time;

(e) Analysis of the vortex in the centrifugal pump cavity:

According to the change relationship of the frequency component obtained in step (d) with time, determine whether there is a vortex or vortex flow phenomenon inside the centrifugal pump: when the frequency is low, it means that the vortex rotates at a slower speed and the vortex shape is larger; when the frequency is high When , it means that the vortex belt rotates faster and the shape of the vortex belt is smaller; when the frequency changes from low to high, it means that the large vortex belt is broken into multiple small vortex belts;

(f) Adjustment of centrifugal pump running state:

According to the analysis result of step (e), adjust the rotational speed of the valve or the centrifugal pump, so that the broadband frequency amplitude becomes smaller, the bandwidth narrows, and the periodic evolution characteristic disappears; the centrifugal pump enters into a good operating state.

The detecting position of the centrifugal pump is the suction chamber of the pump body of the centrifugal pump or the wall surface of the water inlet pipeline.

The step (a) collects the pressure pulsation time domain signal in the centrifugal pump chamber through the following scheme: a pressure measuring hole is set near the inlet of the centrifugal pump pump body, a pressure pulsation sensor is installed through the connection line, and the corresponding acquisition hardware and software system are used to record Pressure pulsation time domain signal in the pump cavity.

Compared with prior art, the beneficial effect of the present invention is:

The invention can quantitatively analyze the performance characteristics of the pressure pulsation frequency generated by the vortex in the cavity of the centrifugal pump, and provide the change of the size of the traveling vortex and the main frequency components with time.

The present invention only needs to arrange pressure pulsation sensors at several points on the water suction chamber of the pump body or the wall surface of the water inlet pipeline, and by analyzing the time-frequency characteristics of the pressure pulsation, it can be judged whether there is a flow phenomenon such as vortex or vortex belt inside the centrifugal pump, and it can be judged whether the vortex occurs It can move, and can regularly and quantitatively reflect the vortex shape changes in the pump chamber; it is of great significance to guide the stable operation of centrifugal pumps; the concept of pressure pulsation "broadband frequency" is proposed in this method, and the time-frequency characteristic analysis method is introduced. It enriches and perfects the existing centrifugal pump pressure pulsation evaluation system. Using the method can ensure that the vortex flow at the inlet of the centrifugal pump is in a relatively ideal state, thereby prolonging the service life of the centrifugal pump, ensuring that the centrifugal pump has higher efficiency and saving energy consumption.

Description of drawings

Fig. 1 is the technical roadmap of the centrifugal pump adjustment method based on the pressure pulsation time-frequency characteristic analysis of the present invention;

Fig. 2 is a schematic diagram of pressure pulsation acquisition in the present invention;

Fig. 3 is the pressure pulsation time-domain diagram of the present invention;

Fig. 4 is the pressure pulsation frequency domain figure of the present invention;

Fig. 5 is the schematic diagram of the Gaussian distribution envelope definition broadband frequency method that the present invention adopts;

Fig. 6 is a schematic diagram of broadband frequency characteristic analysis of the present invention;

Fig. 7 is a schematic diagram of the time-frequency distribution of the present invention;

Fig. 8 is a schematic diagram of the ridge information extraction method of the present invention.

The reference signs therein are:

1 pump body

2 pressure holes

3 cables

4 pressure pulsation sensor

detailed description

The present invention is further described below in conjunction with embodiment.

The technical solution of the present invention is to collect the pressure pulsation time-domain signal at the specific measuring point of the centrifugal pump, and perform FFT transformation (Fast Fourier Transformation) on the obtained pressure pulsation time-domain signal, that is, the fast Fourier transform, which is the discrete Fourier transform The fast algorithm adopts the Gaussian distribution envelope with a continuous frequency band with high pressure amplitude to quantitatively obtain its center frequency, frequency bandwidth and other parameters, and uses the time-frequency distribution and ridge information extraction technology in modern digital signal analysis to give different time bandwidths Variation characteristics of frequency components.

In the present invention, "broadband frequency" refers to the sum of continuous frequencies with high pressure amplitude in the frequency domain diagram, distributed in bands, usually in the shape of a "hill".

As shown in Figure 2, the schematic diagram of the pressure pulsation acquisition of the present invention, a pressure-taking hole 2 is set near the inlet of the pump body 1 of the centrifugal pump, a pressure pulsation sensor 4 is installed through the connection line 3, and the corresponding acquisition hardware and software system are used to record the pressure in the pump chamber. The time-domain signal of pressure fluctuations.

As shown in Figure 1, it is a technical roadmap of the vortex analysis method in the cavity of a centrifugal pump based on the pressure pulsation time-frequency characteristics of the present invention, and the method includes the following steps:

(a) Acquisition of pressure pulsation in the pump chamber to obtain the time domain of pressure pulsation:

A pressure pulsation sensor 4 is set at the detection position of the centrifugal pump, and the pressure pulsation sensor 4 outputs the water pressure pulsation signal to the acquisition card, and is converted into a digital signal by a processor connected to the acquisition card, and the digital signal is the pressure pulsation at the detection position of the centrifugal pump Time Domain.

As shown in Fig. 3, the time-domain diagram of the pressure pulsation of the present invention, the abscissa is time, and the ordinate is the pressure pulsation coefficient, which physically shows that at a certain instant, the static pressure generated by the water at the measuring point is caused by the action of the sensor. At this time, the static pressure value is expressed by the pressure fluctuation coefficient Cp, Among them, u ₂ is the peripheral speed of the impeller outlet, m/s; p _i is the transient static pressure value, kPa; is the average static pressure value, kPa; ρ is the density of water, kg/m3.

(b) Spectrum analysis of pressure pulsation:

FFT transform is performed on the pressure pulsation time domain of the detection position of the centrifugal pump obtained in step (a), to obtain the pressure pulsation frequency domain.

As shown in Figure 4 is the pressure pulsation frequency domain diagram of the present invention, the abscissa is the frequency value, and the ordinate is the amplitude of the corresponding frequency, from Figure 4, it can be found that there is an axial frequency of a single frequency component in the frequency domain, and A wide-band frequency component in which multiple frequency components appear consecutively. However, the pressure pulsation frequency domain can only physically represent all the frequency components of the pressure pulsation within the test time, and cannot reflect when each frequency component appears and the order in which they appear; Gaussian distribution envelope and further time-frequency distribution and ridge information extraction.

(c) Analysis of pressure pulsation broadband frequency characteristics (identification of vortex or vortex belt components):

Carry out Gaussian distribution envelope to the continuous broadband frequency of high pressure amplitude in the pressure pulsation frequency domain that step (b) obtains, fit and obtain central frequency and broadband frequency; As shown in Figure 5, the Gaussian distribution definition that the present invention adopts Schematic diagram of the broadband frequency method, which performs a Gaussian distribution envelope on the continuous frequency band from 0 to 40 Hz in Figure 4, and the formula used is:

Where x represents the frequency component of the broadband frequency, y represents the amplitude corresponding to the frequency, y ₀ is the deviation height, then the envelope result parameter x _c is the center frequency, w is the bandwidth, and A is the Gaussian distribution envelope amplitude , e is the natural base. This process is just a quantitative definition of the overall characteristics of the broadband frequency, providing parameters for comparison between different types of eddies, setting y ₀ to 0, and using matlab multi-parameter fitting technology to obtain the center frequency x _c , broadband frequency x, Gaussian distribution package Network amplitude A.

As shown in Figure 6, the analysis schematic diagram of the broadband frequency characteristics of the present invention, the results show that in addition to the axial frequency component in the frequency spectrum, there is also a continuous low-frequency broadband component with high pressure amplitude, and the low-frequency broadband component is fitted according to the definition in Figure 5 , a low-frequency broadband frequency with a center frequency of 13.31 Hz and a frequency bandwidth of 22 Hz is obtained by fitting, as shown by the dotted line in the figure. After introducing the concept of broadband frequency, this kind of continuous frequency band with continuous high amplitude can be quantitatively analyzed. The broadband frequency components are associated with unstable larger-scale vortices, whose shape may change over time, resulting in changes in the frequency of pressure fluctuations in its vicinity.

(d) Characteristic analysis of broadband frequency components changing with time (characteristic analysis of wandering vortex):

Carry out adaptive optimization and time-frequency distribution on the broadband frequency obtained in step (c), obtain the change of frequency and its amplitude in time, and extract the frequency components whose amplitude is greater than 50% to 70% of the highest intensity level as ridge information , to get the relationship of its frequency components changing with time.

As shown in Figures 7 and 8, time-frequency distribution and ridge information extraction are further performed on the broadband frequency in Figure 6 . In order to solve the problem that the analysis of the spectrum characteristics in (b) and (c) cannot quantitatively reveal the occurrence time of each frequency component, adaptive optimization and time-frequency distribution methods are firstly used. The analysis results are shown in Figure 7, and the abscissa represents time, The vertical axis represents frequency, and the colors represent intensity levels. Any point in the figure can represent the intensity of a specific frequency component at a certain moment. In order to focus on the characteristics of vortex flow, the highest intensity level of 50% to 70% is used for ridge information extraction, that is, the frequency greater than 50% to 70% of the highest intensity level will be represented as the appearance of red dots, as shown in Figure 8. The relationship of frequency components with time obtained in the broadband frequency bandwidth range can be used as an important quantitative feature of vortex evolution.

(e) Analysis of the vortex in the centrifugal pump cavity:

According to the change relationship of the broadband frequency component obtained in step (d) with time, judge whether there is a vortex or vortex flow phenomenon inside the centrifugal pump: when the frequency is low, it means that the vortex rotates at a slower speed and the vortex shape is larger; when the frequency When it is high, it means that the vortex belt rotates faster and the shape of the vortex belt is smaller; when the frequency changes from low to high, it means that the vortex belt with a large shape is broken into multiple vortex belts with a small shape.

It is found from Figures 7 and 8 that the frequency components of the pressure pulsation will change slightly. It can be seen that the frequency of the pressure pulsation changes from 5Hz to 40Hz (or decreases from 40Hz to 5Hz) within 0.1s, which is the result of the momentary change of the vortex shape in the pump chamber. When the frequency is close to 5Hz, it means that the vortex belt rotates slowly and the shape of the vortex belt is large; when the frequency is close to 40Hz, it means that the vortex belt rotates fast and the shape of the vortex belt is small. When the detected frequency changes from small to large, it means that the large vortex is broken into multiple small vortex, and vice versa. In this way, the internal flow state of the centrifugal pump can be effectively monitored to guide the stable operation of the centrifugal pump.

(f) Adjustment of centrifugal pump running state:

According to the analysis result of step (e), adjust the rotational speed of the valve or the centrifugal pump, so that the broadband frequency amplitude becomes smaller, the bandwidth narrows, and the periodic evolution characteristic disappears; the centrifugal pump enters into a good operating state.

It is analyzed that there is a vortex or vortex flow phenomenon inside the centrifugal pump. When the frequency changes from low to high, the large vortex is broken into multiple small vortexes. At this time, the outlet valve of the centrifugal pump can be increased or the centrifugal pump can be lowered. The method of operating speed adjusts the operating state of the centrifugal pump. When it is detected that the amplitude of the broadband frequency becomes smaller, the bandwidth narrows, and the periodic evolution characteristics disappear, it indicates that the centrifugal pump has entered a good operating state.

The invention provides a centrifugal pump adjustment method based on pressure pulsation time-frequency characteristic analysis for monitoring the operation status of a centrifugal pump in a large pumping station. It is only necessary to open a small hole at the proper position of the centrifugal pump inlet, install a pressure pulsation sensor, and collect and obtain time domain signals. On this basis, the technology of the present invention can be used to quantitatively determine whether there is an unstable vortex flow in the centrifugal pump cavity. And quantitatively characterize the strength and evolution of the vortex flow. When a vortex flow with broadband frequency, large bandwidth, high amplitude, and obvious periodicity is detected, the pump is often in an unfavorable working condition, and it is recommended that the pump station take measures such as adjusting the valve and speed; when the broadband frequency amplitude is detected Smaller, narrower bandwidth, disappearance of periodic evolution characteristics, etc., indicating that the centrifugal pump has entered a good operating state. The use of this technology can ensure that the vortex flow at the inlet of the centrifugal pump is in a relatively ideal state, thereby prolonging the service life of the centrifugal pump, ensuring that the centrifugal pump has high efficiency and saving energy consumption.

The above are the best implementation modes of the present invention. Based on the disclosed content of the present invention, those skilled in the art can obviously think of some similarities and alternatives, all of which should fall within the protection scope of the present invention.

Claims (3)

1. a kind of based on pressure fluctuation time-frequency characteristic analysis centrifugal pump control method it is characterised in that：The method includes as follows Step：

A the pressure fluctuation of () pump chamber gathers, obtain pressure fluctuation time domain：

Pressure pulsation sensor is set in centrifugal pump test position, water pressure fluctuation signal output is adopted by pressure pulsation sensor Truck, and digital signal is converted into by the processor being connected with capture card, this digital signal is exactly centrifugal pump test position Pressure fluctuation time domain；

(b) pressure fluctuation spectrum analyses：

The pressure fluctuation time domain of the centrifugal pump test position that step (a) is obtained carries out FFT, obtains pressure fluctuation frequency Domain；

(c) pressure fluctuation wideband frequency feature analysiss：

The continuous broad band low frequency composition having high pressure amplitude in the pressure fluctuation frequency domain that step (b) is obtained carries out Gauss distribution Envelope, matching obtains mid frequency and wideband frequency；

D () wideband frequency composition changes over feature analysiss：

Adaptive optimization and time-frequency distributions are carried out to the wideband frequency obtaining in step (c), obtain frequency and its amplitude when Between on change, extract amplitude be more than 50%～70% maximum intensity grade frequency content as ridge information, obtain its frequency Composition relation over time；

E () centrifugal pump intracavity whirlpool is analyzed：

The frequency content relation over time being obtained according to step (d), judge inside centrifugal pump with the presence or absence of vortex or Vortex rope flow phenomenon：When frequency is low, represent that vortex rope rotary speed is slower, vortex rope form is larger；When frequency is high, represent vortex rope Rotary speed is very fast, and vortex rope form is less；Frequency by low change to high when, just to be broken for multiple forms little for the big vortex rope of explanation form Vortex rope；

F () centrifugal pump running status is adjusted：

According to the analysis result of step (e), the rotating speed of control valve or centrifugal pump, so that wideband frequency amplitude is diminished, bandwidth narrows, Periodic evolution characteristic disappears；Centrifugal pump enters good running status.

2. according to claim 1 based on pressure fluctuation time-frequency characteristic analysis centrifugal pump control method it is characterised in that： Described centrifugal pump test position is centrifugal pump body suction chamber or inlet pipeline wall.

3. according to claim 1 based on pressure fluctuation time-frequency characteristic analysis centrifugal pump control method it is characterised in that： Described step (a) gathers centrifugal pump cavity pressure pulsation time-domain signal by following scheme：Set near centrifugal pump body import Put pressure tap, pressure pulsation sensor is installed by connecting line, by corresponding acquisition hardware and software system, record in pump chamber Pressure fluctuation time-domain signal.